It looks to me like the chocolate stripes were laid down first, left to set up and then white chocolate poured over that. Then strips were cut and matched together but slightly overlapping. You can see where the stripes are very close but not quite matching all the time.

Or the opposite way, white chocolate laid down first and the milk chocolate swirled over top of it. I can't tell from the picture but if the chocolate is shiny, than it is done the way Carmijok said with the brown chocolate first.